1. Technical Field
The invention relates to a compact structure for an electric compressor, and in particular, to a compact structure for an electric compressor that reduces noise vibration harshness.
2. Discussion
With an increasing need to reduce fuel usage and emissions, companies are constantly pursuing alternative fuel and energy sources. Such pursuit of alternative fuels and energy has resulted in vehicles using either partially or entirely electric motors. For example, increasing numbers of automobiles are being developed as fuel/electric hybrids, plug in hybrids or total electric vehicles. With the electrification of these vehicles, typical accessories, such as the air conditioner must become electrically driven, so that if the engine of a hybrid shuts off, or if the vehicle does not have an engine, the passenger compartment can be kept comfortable.
One of the many challenges posed by electric compressors, is the task of fitting the compressor complete with an electric motor in a package that is the same as a typical belt driven accessory. Failure to accomplish this, results in a power train or vehicle architecture that has to be redesigned, which adds significant cost and complexity to the design. This is best avoided.
A second challenge posed by electric compressors is that Noise Vibration Harshness (NVH) characteristics must be much better than conventional engine driven accessories. Typically, the engine noise of a vehicle will drown out compressor noise. Since the compressor in hybrid and electric vehicles runs without engine operation, there is little or no engine noise to mask the sound of the compressor noise. It is therefore preferable to find another solution that will mask or prevent the compressor noise-noise that would otherwise be a nuisance to a passenger in the vehicle.
In conventional hybrid and electric vehicles, electric compressors are typically used to accomplish cooling of the passenger compartment. Since the package size of the compressor must be small, to fit the vehicle, compressors are typically equipped with a brushless DC motor, which drives the compressor. The brushless motor has an inverter, which converts the DC current from the battery to AC current that drives the rotating motor. Fitting the motor, inverter and compressor into a package that is the same as a belt driven compressor is very difficult. Hence, most electric compressors used on vehicles are larger than a belt driven version. As a consequence, the engine or vehicle layout must be altered, which adds significant cost and complexity to the vehicle. Additionally, typical electric compressors for vehicles tend to be noisy. To remedy this, the compressors are sometimes outfitted with additional shielding or noise blankets, which add complexity and cost.
As previously discussed, an electric compressor 5 typically includes a tube or cup shaped housing 10 that has the motor and compressor mechanisms stacked inside. This method of construction is shown in FIG. 1. In this figure, the compressor mechanism is supported via a ledge 15a, 15b in the cup shaped housing 10. The compressor mechanism generates vibration while it is in motion. Due to the fact that the compressor and housing are not rigidly connected, the vibration increases, since the rigidity of the compressor support is not large. As a consequence, NVH increases. Additionally, the large cup shaped housing is prone to flexure, which makes vibration generated by the compressor increase due to the bell like nature 20 of the housing as shown in FIG. 2. As illustrated in FIG. 2, the bell like nature of the housing 20 does not rigidly support the compressor, which causes large deflections at 22. Additionally, the cantilevered portion of the bell shaped housing is long, which further reduces rigidity.